Conventionally, in a DC power-supply device that increases an output voltage to be higher than an input voltage and outputs the voltage, there has been proposed a circuit in which a booster circuit is configured to have a reactor, a group of serially connected switching elements, a group of serially connected capacitors, and a diode that prevents backflow from the capacitors, to suppress an increase in withstand voltage of the switching elements due to a boosted voltage. Particularly, there is a technique of driving a three-level inverter using a midpoint voltage and a voltage between both ends of the serially connected capacitors (see, for example, Patent Literatures 1 and 2).